The overall objective of the research is to study the enzymatic initiation of DNA synthesis in mammalian cells and in particular, the mechanism of RNA priming of DNA synthesis. The specific aims of this proposal are: 1. Examine the synthesis of RNA primers by a DNA primase that we have purified from mouse cells. 2. Examine the initiation of DNA synthesis by primase. 3. Study the mechanism of DNA initiation and elongation that may require other enzymes and/or accessory factors with well defined templates as SV40 or artificial replication forks. 4. Explore the use of anti-peptide antibody immunoaffinity methods for purification of primase and for co-purification of other proteins that may interact with primase.